Vegetable Garden Pests and Diseases



Vegetable Garden Pests and Diseases

vegetable garden pests and diseases My remarks on the importance of ensuring that all chemicals applied to food crops are correctly applied (see Fruit Trees and Bushes Pests and Diseases ) should be taken note of here. It is most important that the manufacturer’s instructions should be followed exactly, especially with regard to strengths and times of application.

Most vegetables are liable to attack by pests and diseases, although only a few are likely to prove a menace in the average kitchen garden. Some, such as slugs and mildews, can prove troublesome to crops in general, while others are specific to particular species or groups of crops. Where appropriate, remedies are given in the notes on the crop concerned. Chemical treatments for the control of pests and diseases are continuously being improved and the range available is now very great.

Where possible, use a chemical that is specific to the particular pest or disease which is proving troublesome — but make sure that it is not harmful to the plant in question. Always apply the chemicals exactly according to the manufacturers’ instructions. Remember that they are poisons: do not harvest or eat vegetables treated with them until the chemicals have lost their toxic properties (the waiting period will be given in the manufacturers’ instructions for use); and keep the chemicals out of reach of children. Thoroughly wash all equipment, such as sprayers, cans, rubber gloves, and so on, that has come in contact with the chemicals.

Always keep your vegetable plot free of weeds, which not only consume soil nutriments earmarked for crops but may attract pests and diseases. Although many chemical weedkillers are available, in the small kitchen garden the best way to deal with weeds is to remove them by hand. Make sure to get rid of all their roots, and if possible complete your weeding before these undesirables have had time to set seed. Autumn debris, including the remains of harvested crops, also attracts pests and provides a breeding ground for diseases, so always make a point of clearing away any such unwanted vegetable matter. Much of it will be suitable for converting into compost.


Plant Pests affecting Vegetables

Aphids, see Garden Pests and Diseases of Trees and Shrubs

Cabbage Caterpillars. The larvae of both the Cabbage White Butterfly and the Cabbage Moth feed on the leaves of cabbages and other brassicas in summer, reducing them to skeletons in a few days in a severe attack. Cabbage White Butterflies are creamy-white; the Cabbage Moth is greyish with black markings, and it flies only at night. Spray or dust the plants with derris or DDT and pick the caterpillars off by hand whenever possible.

Cabbage Root Fly. The small white grubs of this fly attack the lower part of the stem or upper roots of cabbages and allied crops, causing the plants to assume a leaden colour and eventually wilt and collapse. The fly, which is not unlike an ordinary housefly, appears from May onwards and the eggs are laid on the stems just below the surface of the ground. Newly planted seedlings are especially liable to be attacked. Dust the seed bed with lindane, and newly planted seedlings with 4 per cent calomel dust, and repeat a fortnight later. Spray affected plants with lindane.

Carrot Fly. Greenish-black flies lay their eggs in the soil during spring and summer and small white maggots hatch out from these and attack the roots, on which canker may later follow. They are most troublesome in late April and throughout May, and late-sown carrots (June — July) often escape damage. Dust naphthalene on the surface soil around plants every 10 days, from thinning time until the end of June.

Celery Fly. The maggot of this fly bores into the leaves of celery and feeds within them. In a bad attack the leaves may be so severely tunnelled that only the skin remains. The larvae are very small, legless, and white or green in colour. Mild attacks can be controlled by picking off and burning affected leaves, but usually it is necessary to spray occasionally from May to August with DDT or BHC. Eelworm. These are tiny transparent eel-like creatures which live within the tissues of some plants, and feed and multiply therein. Potatoes are attacked by an eelworm which produces tiny white cysts on roots and tubers, turns leaves yellow and checks growth. They may also enter onions through the stems, causing swelling and misshapen growth. They can only be seen with the help of a microscope or strong hand lens, and are difficult to control. Fortunately most individual species of eelworm confine their attention to particular crops, which makes control a little easier. Crop rotation comes in here, and where the soil is contaminated the crop concerned should not be grown in the same piece of ground for several years. All affected plants should be destroyed by burning. Weeds which may act as hosts should be kept down.

Flea Beetle. These are small blackish beetles, about 1/8in. long, which jump considerable distances when disturbed. They attack the seedlings and young plants of cabbage, turnip and other plants belonging to the Cruciferae family, riddling the leaves with small circular holes and entirely destroying them if not checked. The beetle is most troublesome on light, sandy soil in dry weather, and one method of preventing an attack is to encourage seedlings to make really good vigorous growth by watering, hoeing and the use of artificial fertilisers. Dust the seedlings occasionally with DDT.

Leatherjackets, see Lawn Pests and Diseases

Onion Fly. The white maggots of this fly attack the young bulbs of onions, eating into them and destroying them. The first indication of such an attack is that the foliage assumes a leaden hue and flags. This pest is not easy to control but dusting the soil with BHC or lindane immediately after planting and again two weeks later will help to discourage an attack.

Slugs, see Garden Pests and Diseases of Bulbs, Corms and Tubers

Wireworm. The larvae of click beetles. The thin worm-like grubs are about 1in. long with hard, shiny yellow skins. They are especially plentiful in grassland, and where this is dug up, and planted with vegetables, they will attack and feed on potatoes, carrots and other root crops, doing considerable damage. This may be severe in spring and early autumn. They can be trapped by burying pieces of potato or carrots close to the crops, or killed by forking in naphthalene. Seed should be treated with an organo-mercury seed dressing before sowing.


Plant Diseases affecting Vegetable Plants

Botrytis, see Garden Pests and Diseases of Bulbs, Corms and Tubers

Broad Bean Chocolate Spot. This is a form of botrytis which is seen as large dark brown blotches on the leaves, and streaks on the stems. Where the disease appears spray the plants with Bordeaux Mixture.

Club Root. Also known as Finger and Toe and Anbury, this fungal disease affects cabbages and other brassicas, making the roots swollen, distorted and almost devoid of fibres. Infected plants must be burnt and the soil not planted with brassicas or other plants affected by the disease for at least four years. Soil that is acid or ‘sour’ is highly favourable to the development of the disease, and the soil should be given lime at the rate of 1lb. per square yard, as soon as it is cleared, and similar dressings should be given annually for three or four years. Dip the roots of the plants before planting into a paste made of 4oz. calomel dust and water, or sprinkle calomel dust into the planting holes.

Cucumber Foot Rot. This disease causes the stem to rot just above soil level, the flow of sap then being checked and causing the plant to wilt suddenly and collapse. It is often caused by over-deep planting (the cotyledon or seed leaves must be kept above soil level when planting) and by water collecting at the base of the stems. A way of overcoming over-moist conditions at the base of the stem is to plant the cucumbers on low mounds. When trouble occurs dust heavily around the stems with copper dust.

Damping Off, see Lawn Pests and Diseases

Mildew. This fungal disease attacks numerous crops. The surface of the leaves, and possibly also the stems, are covered with whitish or greyish patches that often appear to be mealy. Mildew is most likely to occur when the atmosphere is very moist and the soil is rather dry, and it is common in August and September. Remedial measures include dusting the leaves with flowers of sulphur or spraying with colloidal sulphur, Bordeaux Mixture or zineb. Brassicas, lettuce, spinach, peas and onions in particular are liable to be attacked.

Potato Blight. This disease of potatoes and tomatoes is unfortunately all too prevalent, but is unlikely to cause trouble on early potatoes as it does not usually affect plants until early July in most parts of the country in a normal season. It is usually reported in the West Country about mid-June, spreading eastwards thereafter. It is easily identified as brown or black patches on the leaves, these spreading to the stems as the disease progresses, and the tubers (of the potatoes) or fruits (tomatoes) become marked with decaying brown patches. A preventive spray of Bordeaux Mixture or zineb should be made just before an attack is likely, this being repeated at fortnightly intervals until the middle of September.

Potato Scab. This trouble is identified by the brown, flaky scabs on the skin of the tuber. The culinary value of the tubers is not affected, but it does, however, make them much more difficult to clean and peel satisfactorily. It is likely to occur in soils containing a lot of lime and surrounding the planting sets with peat or leafmould will help to combat this trouble.

Potato Wart Disease. This is the most serious disease of potatoes, readily recognised by wartlike outgrowths on the tubers. There is no known cure, but many varieties are immune to it, and where the disease is at all prevalent, these varieties should be grown exclusively. The flesh is attacked also and the potato may be destroyed completely. If this disease is experienced the Ministry of Agriculture, Fisheries and Food must be informed.

Parsnip Canker. The brown or sometimes black patches seen on parsnips round the top of the roots are produced by canker, and where the trouble has occurred previously, give the soil a generous application of lime before sowing seed. Do not grow on heavily manured ground. It is sometimes started off by injuries originally caused by the carrot fly and in this respect an application of 4 per cent Calomel dust would be helpful.

Soft Rot. A bacterial disease which attacks many vegetables and is sometimes caused by deficiencies of such trace elements as boron and magnesium. The plant tissue turns brown and decays rapidly, becoming markedly wet and slimy, and sometimes foul-smelling. It eventually disintegrates into a liquid mess. Once infected there is no cure, but growing the plants strongly, keeping the ground clean, avoiding injury to roots or top growth and controlling slugs and other pests will do much to prevent this trouble occurring.

Tomato Pests and Diseases – see Tomato Plant Pests and Diseases

Control consists of keeping the greenhouse shaded and as warm as possible and plants frequently damped overhead rather than watered at the roots. If the house can be kept at a temperature of at least 25° C (77° F) for a fortnight a complete cure may sometimes be affected. Dead plants must be removed immediately and if new ones are to take their place the soil should be watered with Cheshunt Compound before planting.

02. December 2010 by Dave Pinkney
Categories: Fruit & Veg, Garden Management, Pests and Diseases | Tags: | Comments Off on Vegetable Garden Pests and Diseases

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